Systems and methods for re-establishing a connection

ABSTRACT

A method for re-establishing a connection by a user equipment (UE) is described. The method includes establishing a first connection between the UE and an Evolved Universal Terrestrial Radio Access Network (E-UTRAN). The method also includes establishing a second connection between the UE and the E-UTRAN. The method also includes informing the E-UTRAN of a failure of the second connection when a failure of the second connection is detected.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/079,645, entitled “SYSTEMS AND METHODS FOR RE-ESTABLISHING ACONNECTION,” filed on Mar. 24, 2016, which is a divisional of U.S.patent application Ser. No. 13/890,987, entitled “SYSTEMS AND METHODSFOR RE-ESTABLISHING A CONNECTION,” filed on May 9, 2013, both of whichare incorporated by reference herein, in their entireties.

TECHNICAL FIELD

The present disclosure relates generally to communication systems. Morespecifically, the present disclosure relates to systems and methods forre-establishing a connection.

BACKGROUND

Wireless communication devices have become smaller and more powerful inorder to meet consumer needs and to improve portability and convenience.Consumers have become dependent upon wireless communication devices andhave come to expect reliable service, expanded areas of coverage andincreased functionality. A wireless communication system may providecommunication for a number of wireless communication devices, each ofwhich may be serviced by a base station. A base station may be a devicethat communicates with wireless communication devices.

As wireless communication devices have advanced, improvements incommunication capacity, speed, flexibility and efficiency have beensought. However, improving communication capacity, speed, flexibilityand efficiency may present certain problems.

For example, wireless communication devices may communicate with one ormore devices using a communication structure. However, the communicationstructure used may offer limited flexibility and efficiency. Asillustrated by this discussion, systems and methods that improvecommunication flexibility and efficiency may be beneficial.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating dual connectivity between a userequipment (UE) and multiple evolved Node Bs (eNBs);

FIG. 2 is a thread diagram illustrating one configuration of asuccessful connection re-establishment procedure;

FIG. 3 is a thread diagram illustrating one configuration of a failedconnection re-establishment procedure;

FIG. 4 is a block diagram illustrating one configuration of one or moreeNBs and one or more UEs in which systems and methods forre-establishing a connection may be implemented;

FIG. 5 is a flow diagram illustrating one configuration of a method forre-establishing a connection by a UE;

FIG. 6 is a flow diagram illustrating one configuration of a method forre-establishing a connection by an eNB;

FIG. 7 is a block diagram illustrating an addition of a secondconnection between a UE and an eNB;

FIG. 8 is a block diagram illustrating a handover of a second connectionbetween a UE and multiple eNBs;

FIG. 9 is a block diagram illustrating a failure of a second connectionbetween a UE and an eNB;

FIG. 10 is a block diagram illustrating one configuration of an E-UTRANand a UE in which systems and methods for re-establishing a connectionmay be implemented;

FIG. 11 is a block diagram illustrating one configuration of a UE andmultiple eNBs in which systems and methods for re-establishing aconnection may be implemented;

FIG. 12 is a block diagram illustrating another configuration of a UEand multiple eNBs in which systems and methods for re-establishing aconnection may be implemented;

FIG. 13 is a block diagram illustrating another configuration of a UEand multiple eNBs in which systems and methods for re-establishing aconnection may be implemented;

FIG. 14 is a flow diagram illustrating a more specific configuration ofa method for re-establishing a connection by a UE;

FIG. 15 is a flow diagram illustrating a more specific configuration ofa method for re-establishing a connection by an eNB;

FIG. 16 is a thread diagram illustrating one configuration forre-establishing a connection;

FIG. 17 is a thread diagram illustrating another configuration forre-establishing a connection;

FIG. 18 illustrates various components that may be utilized in a UE;

FIG. 19 illustrates various components that may be utilized in an eNB;

FIG. 20 is a block diagram illustrating one configuration of a UE inwhich systems and methods for re-establishing a connection may beimplemented; and

FIG. 21 is a block diagram illustrating one configuration of an eNB inwhich systems and methods for re-establishing a connection may beimplemented.

DETAILED DESCRIPTION

A method for re-establishing a connection by a user equipment isdescribed. The method includes establishing a first connection betweenthe UE and an E-UTRAN. The method also includes establishing a secondconnection between the UE and the E-UTRAN. The method further includesinforming the E-UTRAN of a failure of the second connection when afailure of the second connection is detected.

The method may include determining whether to use the first connectionor the second connection to inform the E-UTRAN of the failure of thesecond connection. The method may include informing a suitable cellabout the failure of the second connection if the suitable cell isdetected. The method may also include informing a cell of the firstconnection about the failure of the second connection if the suitablecell is not detected. The method may include selecting the suitable cellfor a re-established second connection from a prepared re-establishmentcandidate cells list. The method may include releasing the secondconnection if the suitable cell is not detected.

The failure of the second connection may be at least one of an additionof connection failure, a handover failure, a radio link failure, anEvolved Universal Terrestrial Access (E-UTRA) mobility failure, anintegrity check failure and a reconfiguration failure. The method mayinclude indicating a cause of the failure.

A method for re-establishing a connection by an evolved Node B (eNB) isdescribed. The method includes receiving information about a failure ofa second connection between a UE and an E-UTRAN. The method alsoincludes determining whether UE context information is stored on theeNB. The method also includes re-establishing the second connection whenUE context information is stored on the eNB. The method further includesinforming another eNB of the E-UTRAN about the re-established secondconnection.

The UE may have a first connection with the E-UTRAN. The method mayinclude providing a prepared re-establishment candidate cells list forthe re-established second connection. The prepared re-establishmentcandidate cells may include UE context information for there-established second connection.

The method may include preparing UE context information for there-established second connection. The failure of the second connectionis at least one of an addition of connection failure, a handoverfailure, a radio link failure, an E-UTRA mobility failure, an integritycheck failure and a reconfiguration failure.

A UE for re-establishing a connection is described. The UE includes aprocessor. The UE also includes memory in electronic communication withthe processor. Instructions stored in the memory are executable toestablish a first connection between the UE and an E-UTRAN. Theinstructions are also executable to establish a second connectionbetween the UE and the E-UTRAN. The instructions are further executableto inform the E-UTRAN of a failure of the second connection when afailure of the second connection is detected.

An eNB for re-establishing a connection is described. The eNB includes aprocessor. The eNB also includes memory stored in electroniccommunication with the processor. Instructions stored in the memory areexecutable to receive information about a failure of a second connectionbetween a UE and an E-UTRAN. The instructions are further executable todetermine whether UE context information is available to the eNB. Theinstructions are also executable to re-establish the second connectionwhen UE context information is available to the eNB. The instructionsare further executable to inform another eNB of the E-UTRAN about there-established second connection.

The 3rd Generation Partnership Project, also referred to as “3GPP,” is acollaboration agreement that aims to define globally applicabletechnical specifications and technical reports for third and fourthgeneration wireless communication systems. The 3GPP may definespecifications for next generation mobile networks, systems and devices.

3GPP Long Term Evolution (LTE) is the name given to a project to improvethe Universal Mobile Telecommunications System (UMTS) mobile phone ordevice standard to cope with future requirements. In one aspect, UMTShas been modified to provide support and specification for the EvolvedUniversal Terrestrial Radio Access (E-UTRA) and Evolved UniversalTerrestrial Radio Access Network (E-UTRAN).

At least some aspects of the systems and methods disclosed herein may bedescribed in relation to the 3GPP LTE, LTE-Advanced (LTE-A) and otherstandards (e.g., 3GPP Releases 8, 9, 10, 11 and/or 12). However, thescope of the present disclosure should not be limited in this regard. Atleast some aspects of the systems and methods disclosed herein may beutilized in other types of wireless communication systems.

A wireless communication device may be an electronic device used tocommunicate voice and/or data to a base station, which in turn maycommunicate with a network of devices (e.g., a public switched telephonenetwork (PSTN), the Internet, etc.). In describing systems and methodsherein, a wireless communication device may alternatively be referred toas a mobile station, a user equipment (UE), an access terminal, asubscriber station, a mobile terminal, a remote station, a userterminal, a terminal, a subscriber unit, a mobile device, etc. Examplesof wireless communication devices include cellular phones, smart phones,personal digital assistants (PDAs), laptop computers, netbooks,e-readers, wireless modems, etc. In 3GPP specifications, a wirelesscommunication device is typically referred to as a UE. However, as thescope of the present disclosure should not be limited to the 3GPPstandards, the terms “UE” and “wireless communication device” may beused interchangeably herein to mean the more general term “wirelesscommunication device.”

In 3GPP specifications, a base station is typically referred to as aNode B, an eNB, a home enhanced or evolved Node B (HeNB) or some othersimilar terminology. As the scope of the disclosure should not belimited to 3GPP standards, the terms “base station,” “Node B,” “eNB,”and “HeNB” may be used interchangeably herein to mean the more generalterm “base station.” Furthermore, one example of a “base station” is anaccess point. An access point may be an electronic device that providesaccess to a network (e.g., Local Area Network (LAN), the Internet, etc.)for wireless communication devices. The term “communication device” maybe used to denote both a wireless communication device and/or a basestation.

It should be noted that as used herein, a “cell” may be anycommunication channel that is specified by standardization or regulatorybodies to be used for International Mobile Telecommunications-Advanced(IMT-Advanced) and all of it or a subset of it may be adopted by 3GPP aslicensed bands (e.g., frequency bands) to be used for communicationbetween an eNB and a UE. In 3GPP, the term “cell” may refer to acoverage area of an eNB and/or an eNB serving this coverage area,depending on the context in which the term is used. “Configured cells”are those cells of which the UE is aware and is allowed by an eNB totransmit or receive information. “Configured cell(s)” may be servingcell(s). The UE may receive system information and perform the requiredmeasurements on all configured cells. “Configured cell(s)” may consistof a primary cell and no, one, or more secondary cell(s). “Activatedcells” are those configured cells on which the UE is transmitting andreceiving. That is, activated cells are those cells for which the UEmonitors the physical downlink control channel (PDCCH) and in the caseof a downlink transmission, those cells for which the UE decodes aphysical downlink shared channel (PDSCH). “Deactivated cells” are thoseconfigured cells that the UE is not monitoring the transmission PDCCH.It should be noted that a “cell” may be described in terms of differingdimensions. For example, a “cell” may have temporal, spatial (e.g.,geographical) and frequency characteristics.

As used herein, the term “connection” may refer to a communication linkbetween a UE and an E-UTRAN. As used herein, the terms “radioconnection,” “connection,” “radio interface” and “interface” may be usedinterchangeably.

The systems and methods described herein may enhance carrieraggregation. In carrier aggregation, a single eNB may be assumed toprovide multiple serving cells for a UE. Even in scenarios where two ormore cells may be aggregated (e.g., a macro cell aggregated with remoteradio head (RRH) cells), the cells may be controlled (e.g., scheduled)by a single eNB. However, in a small cell deployment scenario, each node(e.g., eNB, RRH, etc.) may have its own independent scheduler. Toutilize the radio resources of both nodes efficiently, a UE may connectto two or more nodes that have different schedulers.

In one configuration, for a UE to connect to two nodes (e.g., eNBs) thathave different schedulers, multi-connectivity between the UE and theE-UTRAN may be utilized. For example, in addition to Rel-11 operation, aUE operating according to the Rel-12 standard may be configured withmulti-connectivity (which may be referred to as dual connectivity,inter-eNB carrier aggregation, multi-flow, multi-cell cluster, multi-Uu,etc.). The UE may connect to the E-UTRAN with multiple Uu interfaces, ifconfigured to do so. For instance, the UE may be configured to establishone or more additional radio interfaces (e.g., radio connections) byusing one radio interface (e.g., radio connection). Hereafter, one nodemay be called a primary eNB (PeNB) and another node may be called asecondary eNB (SeNB). A Uu interface (which may be called a primary Uuinterface) may be a connection between the UE and the PeNB. A Uuxinterface (which may be called a secondary Uu interface) may be aconnection between the UE and the SeNB.

In some instances, one of the connections with the E-UTRAN may fail.Accordingly, to utilize the radio resources of both connections, thefailed connection may be re-established. The systems and methodsdescribed herein may allow the UE and the E-UTRAN to re-establish aconnection and to continue efficiently utilizing both connections.

Various examples of the systems and methods disclosed herein are nowdescribed with reference to the Figures, where like reference numbersmay indicate functionally similar elements. The systems and methods asgenerally described and illustrated in the Figures herein could bearranged and designed in a wide variety of different implementations.Thus, the following more detailed description of severalimplementations, as represented in the Figures, is not intended to limitscope, as claimed, but is merely representative of the systems andmethods.

FIG. 1 is a block diagram illustrating dual connectivity between a UE102 and multiple eNBs 160 a-d. The eNBs 160 a-d may be part of anE-UTRAN that provides communication channels to the UE 102. As depictedin FIG. 1, the first eNB 160 a may provide a first cell 196 a thatallows the UE 102 to communicate with the first eNB 160 a. Similarly, asecond eNB 160 b, a third eNB 160 c and a fourth eNB 160 d may provide asecond cell 196 b, a third cell 196 c and a fourth cell 196 d,respectively.

To implement dual connectivity, the UE 102 may establish a firstconnection 107 a with the E-UTRAN via the first eNB 160 a, and mayestablish a second connection 107 b with the E-UTRAN via the second eNB160 b. Dual connectivity between the UE 102 and the E-UTRAN may bebeneficial as it utilizes radio resources of multiple nodes efficiently.

As mentioned above, in some instances, the second connection 107 b maybe lost, for example due to an inability of the UE 102 to comply with areconfiguration request. However, the second connection 107 b may bere-established between the UE 102 and the E-UTRAN. The second connection107 b may be re-established with a cell 196 that has access to UEcontext information 198 b-c corresponding to the second connection 107b. A cell 196 that has access to UE context information 198 a-c may bereferred to as a prepared cell. A cell 196 may have access to UE contextinformation if the eNB that is providing the cell stores the UE contextinformation.

UE context information 198 a-c may be information that allows aconnection to be established between the UE 102 and the E-UTRAN. The UEcontext information 198 a-c may include radio resource control (RRC)context information such as configuration information, configured cellidentifications, security information, etc. The UE context information198 a-c may also include quality of service (QoS) information and UEidentities. The UE context information 198 a-c may be connectionspecific. For example, first connection UE context information 198 a mayallow a first connection 107 a to be established between the UE 102 anda first eNB 160 a. By comparison, second connection UE contextinformation 198 b-c may allow a second connection 107 b to beestablished (or re-established) between the UE 102 and the second eNB160 b or the third eNB 160 c. The second connection UE contextinformation 198 b-c may or may not be the same as the first connectionUE context information 198 a. For example, the second connection UEcontext information 198 b-c may be part of the first connection UEcontext information 198 a. In some cases, the second connection UEcontext information 198 b-c may include additional information that maybe different than the first connection UE context information 198 a.

To establish the first connection 107 a and the second connection 107 b,the first eNB 160 a, the second eNB 160 b and the third eNB 160 c maystore UE context information 198 a-c for the UE 102. More specifically,the first eNB 160 a may store first connection UE context information198 a and the second eNB 160 b and the third eNB 160 c may store secondconnection UE context information 198 b-c. Accordingly, the first cell196 a, the second cell 196 b and the third cell 196 c may be preparedcells for a re-established connection. By comparison, the fourth cell196 d, on account of not having access to UE context information, maynot be a prepared cell for a connection.

FIG. 2 is a thread diagram illustrating one configuration of asuccessful connection re-establishment procedure 200. The UE 202 may bean example of the UE 102 described in connection with FIG. 1. Theprocedure 200 may be initiated after the UE 202 detects a connectionfailure and selects a suitable cell. Selecting a suitable cell may bebased on a measured reference signal received power (RSRP) of a cell.More detail concerning failure detection and suitable cell selectionwill be given below in connection with FIGS. 4-6. Re-establishing aconnection may include resuming signal radio bearer (SRB1) operation,reactivating security, and configuring a primary cell (PCell). If theE-UTRAN 234 accepts the re-establishment, SRB1 operation may resumewhile the operation of other radio bearers (RBs) may remain suspended.The E-UTRAN 234 may reconfigure SRB1 operation, resume data transfer forthis radio bearer (RB) and re-activate access stratum (AS) securitywithout changing algorithms. The UE 202 may be configured so that if ASsecurity has not been activated, the UE 202 does not initiate theprocedure, but instead moves to an idle state.

To initiate the re-establishment, the UE 202 may send 201 a connectionre-establishment request message to the E-UTRAN 234. More specifically,the UE 202 may set the contents of anRRCConnectionReestablishmentRequest message. The connectionre-establishment request message may include one or more fields thatindicate configuration settings of a desired connection. For example,the connection re-establishment request message may include a cell RadioNetwork Temporary Identifier (c-RNTI) field, a physical cell identifierfield, etc. The connection re-establishment request message may alsoidentify a cause of the failure that triggered the re-establishment. TheUE 202 may then submit the connection re-establishment message to atleast one lower layer of the UE 202 (e.g., at least one of a packet dataconvergence protocol (PDCP) layer of the UE 202, a radio link control(RLC) layer of the UE 202, a media access control (MAC) layer of the UE202 or a physical (PHY) layer of the UE 202) for transmission to theE-UTRAN 234.

After receiving the connection re-establishment request message, theE-UTRAN 234 may send 203 a connection re-establishment message to the UE202. More specifically, the E-UTRAN 234 may send 203 anRRCConnectionReestablishment message. The connection re-establishmentmessage may acknowledge the receipt of the connection re-establishmentrequest message and may provide the UE 202 with configurationinformation for a re-established connection. For example, the connectionre-establishment message may include radio resource configurationinformation, integrity protection algorithms, ciphering applicationalgorithms, etc. to be applied by the UE 202 on subsequenttransmissions. The E-UTRAN 234 may be configured so that after sending203 the connection re-establishment message to the UE 202, the E-UTRAN234 does not send any other messages to the UE 202 until the connectionre-establishment complete message has been received.

After receiving the connection re-establishment message, the UE 202 mayimplement the configuration changes indicated in the connectionre-establishment message. The UE 202 may then send 205 a connectionre-establishment complete message to the E-UTRAN 234. More specifically,the UE 202 may set the contents of anRRCConnectionReestablishmentComplete message. The UE 202 may then submitthe connection re-establishment complete message to at least one lowerlayer of the UE 202 (e.g., at least one of a PDCP layer, an RLC layer, aMAC layer or a PHY layer) for transmission to the E-UTRAN 234. Theconnection re-establishment complete message may indicate to the E-UTRAN234 that the connection re-establishment has been successful (e.g., theUE 202 has applied the configuration changes successfully) and thattransmissions between the UE 202 and the E-UTRAN 234 may resume.

FIG. 3 is a thread diagram illustrating one configuration of a failedconnection re-establishment procedure 300. The UE 302 and the E-UTRAN334 may be examples of corresponding elements described in connectionwith FIGS. 1 and 2. The UE 302 may send 301 a connectionre-establishment request message. This may be done as described inconnection with FIG. 2.

After receiving the connection re-establishment request message, theE-UTRAN 334 may send 303 a connection re-establishment reject message tothe UE 302. More specifically, the E-UTRAN 334 may send 303 anRRCConnectionReestablishmentReject message. The connectionre-establishment reject message may indicate to the UE 302 that are-established connection may not be established. Upon receiving theconnection re-establishment reject message, the UE 302 may release theconnection. It should be noted that one or more of the steps describedin connection with FIGS. 2 and 3 may be implemented in accordance with3GPP TS 36.331.

FIG. 4 is a block diagram illustrating one configuration of one or moreeNBs 460 and one or more UEs 402 in which systems and methods forre-establishing a connection may be implemented. The eNBs 460 and theUEs 402 may be examples of the eNBs 160 a-d and the UE 102 described inconnection with FIG. 1. The one or more UEs 402 may communicate with oneor more eNBs 460 using one or more antennas 422 a-n. For example, a UE402 may transmit electromagnetic signals to the eNB 460 and may receiveelectromagnetic signals from the eNB 460 using the one or more antennas422 a-n. The eNB 460 may communicate with the UE 402 using one or moreantennas 480 a-n. It should be noted that one or more of the UEsdescribed herein may be implemented in a single device in someconfigurations. Additionally or alternatively, one or more of the eNBs460 described herein may be implemented in a single device in someconfigurations. In the context of FIG. 4, for instance, a single devicemay include one or more UEs 402 in accordance with the systems andmethods described herein. Additionally or alternatively, one or moreeNBs 460 in accordance with the systems and methods described herein maybe implemented as a single device or multiple devices.

The UE 402 and the eNB 460 may use one or more channels 419, 421 tocommunicate with each other. For example, a UE 402 may transmitinformation or data to the eNB 460 using one or more uplink channels421. Examples of uplink channels 421 include a physical uplink controlchannel (PUCCH) and a physical uplink shared channel (PUSCH), etc. Theone or more eNBs 460 may also transmit information or data to the one ormore UEs 402 using one or more downlink channels 419, for instance.Examples of downlink channels 419 include a PDCCH, a PDSCH, etc. Otherkinds of channels may be used.

Each of the one or more UEs 402 may include one or more transceivers418, one or more demodulators 414, one or more decoders 408, one or moreencoders 450, one or more modulators 454, a data buffer 404 and a UEoperations module 424. For example, one or more reception and/ortransmission paths may be implemented in the UE 402. For convenience,only a single transceiver 418, decoder 408, demodulator 414, encoder 450and modulator 454 are illustrated in the UE 402, though multipleparallel elements (e.g., transceivers 418, decoders 408, demodulators414, encoders 450 and modulators 454) may be implemented.

The transceiver 418 may include one or more receivers 420 and one ormore transmitters 458. The one or more receivers 420 may receive signalsfrom the eNB 460 using one or more antennas 422 a-n. For example, thereceiver 420 may receive and downconvert signals to produce one or morereceived signals 416. The one or more received signals 416 may beprovided to a demodulator 414. The one or more transmitters 458 maytransmit signals to the eNB 460 using one or more antennas 422 a-n. Forexample, the one or more transmitters 458 may upconvert and transmit oneor more modulated signals 456.

The demodulator 414 may demodulate the one or more received signals 416to produce one or more demodulated signals 412. The one or moredemodulated signals 412 may be provided to the decoder 408. The UE 402may use the decoder 408 to decode signals. The decoder 408 may produceone or more decoded signals 406, 410. For example, a first UE-decodedsignal 406 may comprise received payload data, which may be stored in adata buffer 404. A second UE-decoded signal 410 may comprise overheaddata and/or control data. For example, the second UE-decoded signal 410may provide data that may be used by the UE operations module 424 toperform one or more operations.

As used herein, the term “module” may mean that a particular element orcomponent may be implemented in hardware, software or a combination ofhardware and software. However, it should be noted that any elementdenoted as a “module” herein may alternatively be implemented inhardware. For example, the eNB operations module 482 may be implementedin hardware, software or a combination of both.

In general, the UE operations module 424 may enable the UE 402 tocommunicate with the one or more eNBs 460. The UE operations module 424may include a connection failure detection module 426 and a suitablecell selection module 428.

The connection failure detection module 426 may detect a failure of aconnection between the UE 402 and the E-UTRAN 234. For example, theconnection failure detection module 426 may detect a failure of a secondconnection 107 b between the UE 402 and the second eNB 160 b that isincluded in the E-UTRAN 234. After detecting a failure, the UE 402 mayinitiate a connection re-establishment procedure. The connection failuredetection module 426 may detect different types of connection failures.Various examples of failure detection and subsequent initiation of aconnection re-establishment procedure are given as follows.

In one example, the connection failure detection module 426 may detectradio link failure. A radio link failure may include the detection ofphysical layer complications. For example, the UE 402 may receive acertain amount of consecutive “out-of-sync” indications from the PHYlayer. The “out-of-sync” indications may pertain to communicationsbetween the UE 402 and a primary cell (PCell). When physical layercomplications are detected, the UE 402 may start a timer. Uponexpiration of the timer, the UE 402 may determine that radio linkfailure has been detected. In another example, the UE 402 may detectradio link failure upon a random access problem indication from the MAClayer. In yet another example, the UE 402 may detect radio link failureupon indication from the RLC layer that the maximum number ofretransmissions has been reached. In some cases, if access stratum (AS)security has not been activated and the UE 402 has detected failure, theUE 402 may perform certain actions upon leaving a radio resource control(RRC) connected state.

In another example, the connection failure detection module 426 maydetect a handover failure. For example, the UE 402 may receive aconnection reconfiguration message from the eNB 460 that includes ahandover command. If the UE 402 is able to comply with the connectionreconfiguration message, the UE 402 may start a timer. The UE 402 maythen begin synchronizing with a downlink of a target PCell and maygenerate a connection reconfiguration complete message to be submittedto lower layers of transmission (e.g., a MAC layer). The connectionreconfiguration complete message may direct the MAC layer to initiate arandom access procedure. If the MAC layer successfully completes therandom access procedure, the UE 402 may stop the timer. If the MAC layerdoes not complete the random access procedure before the timer expires,the UE 402 may determine that a handover failure has been detected.

Another example of a connection failure may be an Evolved UniversalTerrestrial Radio Access (E-UTRA) mobility failure. For example, a UE402 may attempt to move from a connected state in an E-UTRA to a cellusing another radio access technology (RAT). If the mobility from E-UTRAfails, the UE 402 may detect connection failure. Examples of other RATsmay include Global System for Mobile Communications (GSM) Enhanced DataRates for GSM Evolution (EDGE) Radio Access Network (GERAN), UniversalMobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA)and Code Division Multiple Access 2000 (CDMA2000).

In another example, the connection failure may be an integrity checkfailure. For example, the RRC layer of the UE 402 may receive anintegrity check failure indication from a lower layer of the UE 402.Accordingly, the UE 402 may determine that a connection has failed.

In yet another example, the connection failure may be a reconfigurationfailure. For example, if the UE 402 is unable to comply with aconnection reconfiguration message, the UE 402 may detect a connectionfailure. If access stratum (AS) security has not been activated and theUE 402 has detected failure, the UE 402 may perform certain actions uponleaving an RRC connected state.

After a second connection 107 b with the E-UTRAN 234 has failed, thesuitable cell selection module 428 may select a suitable cell for are-established second connection (not shown). If the suitable cellselection module 428 selects the second cell 196 b, a re-establishmentmay be successful because the second eNB 160 b includes secondconnection UE context information 198 b.

The suitable cell selection module 428 may select the suitable cell froma prepared re-establishment candidate cells list. The preparedre-establishment candidate cells list may include cells that have accessto second connection UE context information 198 b-c (e.g., a list ofprepared cells).

The suitable cell selection module 428 may detect a cell. Detecting acell may include scanning a particular bandwidth or frequency for thecell. When selecting a suitable cell, the UE 402 may determine whetherthe cell that the UE 402 detected is a suitable cell. Determiningwhether a cell is a suitable cell may include determining whether ameasured reference signal received power of the detected cell satisfiesa cell selection criterion.

The UE operations module 424 may provide information 448 to the one ormore receivers 420. For example, the UE operations module 424 may informthe receiver(s) 420 when or when not to receive transmissions based ondownlink scheduling information or a discontinuous reception (DRX)configuration, etc.

The UE operations module 424 may provide information 438 to thedemodulator 414. For example, the UE operations module 424 may informthe demodulator 414 of a modulation pattern anticipated fortransmissions from the eNB 460.

The UE operations module 424 may provide information 436 to the decoder408. For example, the UE operations module 424 may inform the decoder408 of an anticipated encoding for transmissions from the eNB 460.

The UE operations module 424 may provide information 442 to the encoder450. The information 442 may include data to be encoded and/orinstructions for encoding. For example, the UE operations module 424 mayinstruct the encoder 450 to encode transmission data 446 and/or otherinformation 442. The other information 442 may include RRC messages.

The encoder 450 may encode transmission data 446 and/or otherinformation 442 provided by the UE operations module 424. For example,encoding the data 446 and/or other information 442 may involve errordetection and/or correction coding, mapping data to space, time and/orfrequency resources for transmission, multiplexing, etc. The encoder 450may provide encoded data 452 to the modulator 454.

The UE operations module 424 may provide information 444 to themodulator 454. For example, the UE operations module 424 may inform themodulator 454 of a modulation type (e.g., constellation mapping) to beused for transmissions to the eNB 460. The modulator 454 may modulatethe encoded data 452 to provide one or more modulated signals 456 to theone or more transmitters 458.

The UE operations module 424 may provide information 440 to the one ormore transmitters 458. This information 440 may include instructions forthe one or more transmitters 458. For example, the UE operations module424 may instruct the one or more transmitters 458 when to transmit asignal to the eNB 460. The one or more transmitters 458 may upconvertand transmit the modulated signal(s) 456 to one or more eNBs 460.

The eNB 460 may include one or more transceivers 476, one or moredemodulators 472, one or more decoders 466, one or more encoders 409,one or more modulators 413, a data buffer 462 and an eNB operationsmodule 482. For example, one or more reception and/or transmission pathsmay be implemented in an eNB 460. For convenience, only a singletransceiver 476, decoder 466, demodulator 472, encoder 409 and modulator413 are illustrated in the eNB 460, though multiple parallel elements(e.g., transceivers 476, decoders 466, demodulators 472, encoders 409and modulators 413) may be implemented.

The transceiver 476 may include one or more receivers 478 and one ormore transmitters 417. The one or more receivers 478 may receive signalsfrom the UE 402 using one or more antennas 480 a-n. For example, thereceiver 478 may receive and downconvert signals to produce one or morereceived signals 474. The one or more received signals 474 may beprovided to a demodulator 472. The one or more transmitters 417 maytransmit signals to the UE 402 using one or more antennas 480 a-n. Forexample, the one or more transmitters 417 may upconvert and transmit oneor more modulated signals 415.

The demodulator 472 may demodulate the one or more received signals 474to produce one or more demodulated signals 470. The one or moredemodulated signals 470 may be provided to the decoder 466. The eNB 460may use the decoder 466 to decode signals. The decoder 466 may produceone or more decoded signals 464, 468. For example, a first eNB-decodedsignal 464 may comprise received payload data, which may be stored in adata buffer 462. A second eNB-decoded signal 468 may comprise overheaddata and/or control data. For example, the second eNB-decoded signal 468may provide data (e.g., PUSCH transmission data) that may be used by theeNB operations module 482 to perform one or more operations.

In general, the eNB operations module 482 may enable the eNB 460 tocommunicate with the one or more UEs 402. The eNB operations module 482may include a UE context information detection module 432, a UE contextinformation preparation module 494 and a prepared re-establishmentcandidate cells list generation module 484.

The UE context information detection module 432 may detect whether UEcontext information 198 a-c is stored on the eNB 460. For example,referring to FIG. 1, a UE context information detection module (notshown) on the second eNB 160 b may detect whether second connection UEcontext information 198 b-c is stored on the second eNB 160 b. Becausethe second eNB 160 b does include second connection UE contextinformation 198 b, the second cell 196 b may be a prepared cell and maybe in a prepared re-establishment candidate cells list.

If the UE context information detection module 432 detects that secondconnection UE context information 198 b-c is stored on the eNB 460, theeNB 460 may re-establish the second connection 107 b with the UE 402. Bycomparison, if the UE context information detection module 432 does notdetect that second connection UE context information 198 b-c is storedon the eNB 460, the second connection 107 b may not be re-established.

An example of detecting UE context information 198 a-c is given asfollows. The eNB 460 may receive a connection re-establishment requestmessage from the UE 402 that includes second connection UE contextinformation (e.g., a ue_Identity field) for the UE 402. The eNB 460 maythen compare the received UE context information with UE contextinformation stored on the eNB 460. If the received UE contextinformation matches stored UE context information, the eNB 460 mayverify, and grant access to, the UE 402. More specifically, if aue_Identity field in the received UE context information matches aue_Identity field in stored UE context information, the eNB 460 maygrant access to the UE 402.

The UE context information preparation module 494 may prepare the UEcontext information. For example, referring to FIG. 1, the first eNB 160a may attempt to add a second connection 107 b between the UE 102 andthe E-UTRAN 234 (e.g., via the second eNB 160 b). In this example, a UEcontext information preparation module (not shown) on the first eNB 160a may provide second connection UE context information 198 b to thesecond eNB 160 b. In another example, during a handover procedure, a UEcontext information preparation module (not shown) on the first eNB 160a may provide second connection UE context information 198 c to thethird eNB 160 c. In another example of a handover procedure, a UEcontext information preparation module (not shown) on the second eNB 160b may provide second connection UE context information 198 c to thethird eNB 160 c. In some cases, the UE context information preparationmodule 494 may provide UE context information when there is apossibility of a failure around the region of another eNB 460.

The prepared re-establishment candidate cells list generation module 484may generate a list of candidate cells for a re-established secondconnection 107 b. The candidate cells may be cells that have access tosecond connection UE context information 198 b-c (e.g., a list ofprepared cells). The prepared re-establishment candidate cells list maybe signaled to the UE 402 via RRC signaling or a broadcast transmission.From this list, the UE 402 may select a suitable cell for are-established second connection (not shown).

The eNB operations module 482 may provide information 490 to the one ormore receivers 478. For example, the eNB operations module 482 mayinform the receiver(s) 478 when or when not to receive transmissions.

The eNB operations module 482 may provide information 488 to thedemodulator 472. For example, the eNB operations module 482 may informthe demodulator 472 of a modulation pattern anticipated fortransmissions from the UE(s) 402.

The eNB operations module 482 may provide information 486 to the decoder466. For example, the eNB operations module 482 may inform the decoder466 of an anticipated encoding for transmissions from the UE(s) 402.

The eNB operations module 482 may provide information 401 to the encoder409. The information 401 may include data to be encoded and/orinstructions for encoding. For example, the eNB operations module 482may instruct the encoder 409 to encode transmission data 405 and/orother information 401. The other information 401 may include RRCmessages.

The encoder 409 may encode transmission data 405 and/or otherinformation 401 provided by the eNB operations module 482. For example,encoding the data 405 and/or other information 401 may involve errordetection and/or correction coding, mapping data to space, time and/orfrequency resources for transmission, multiplexing, etc. The encoder 409may provide encoded data 411 to the modulator 413. The transmission data405 may include network data to be relayed to the UE 402.

The eNB operations module 482 may provide information 403 to themodulator 413. This information 403 may include instructions for themodulator 413. For example, the eNB operations module 482 may inform themodulator 413 of a modulation type (e.g., constellation mapping) to beused for transmissions to the UE(s) 402. The modulator 413 may modulatethe encoded data 411 to provide one or more modulated signals 415 to theone or more transmitters 417.

The eNB operations module 482 may provide information 492 to the one ormore transmitters 417. This information 492 may include instructions forthe one or more transmitters 417. For example, the eNB operations module482 may instruct the one or more transmitters 417 when to (or when notto) transmit a signal to the UE(s) 402. The one or more transmitters 417may upconvert and transmit the modulated signal(s) 415 to one or moreUEs 402.

It should be noted that one or more of the elements or parts thereofincluded in the eNB(s) 460 and UE(s) 402 may be implemented in hardware.For example, one or more of these elements or parts thereof may beimplemented as a chip, circuitry or hardware components, etc. It shouldalso be noted that one or more of the functions or methods describedherein may be implemented in and/or performed using hardware. Forexample, one or more of the methods described herein may be implementedin and/or realized using a chipset, an application-specific integratedcircuit (ASIC), a large-scale integrated circuit (LSI) or integratedcircuit, etc.

FIG. 5 is a flow diagram illustrating one configuration of a method 500for re-establishing a connection by a UE 102. The UE 102 may establish502 a first connection 107 a between the UE 102 and an E-UTRAN 234. Forexample, the UE 102 may establish 502 a first connection 107 a with thefirst eNB 160 a of the E-UTRAN 234. In one configuration, the UE 102 mayconnect to the first eNB 160 a with a Uu interface. Via the firstconnection 107 a, the UE 102 may send information to and receiveinformation from the E-UTRAN 234.

Similarly, the UE 102 may establish 504 a second connection 107 bbetween the UE 102 and the E-UTRAN 234. For example, the UE 102 mayestablish 504 a second connection 107 b with the second eNB 160 b of theE-UTRAN 234. The UE 102 may connect to the second eNB 160 b with a Uuxinterface. Via the second connection 107 b, the UE 102 may sendinformation to and receive information from the E-UTRAN 234.

The UE 102 may detect 506 a failure of the second connection 107 b. Forexample, the UE 102 may detect 506 one or more of a radio link failure,a handover failure, an E-UTRA mobility failure, an integrity checkfailure and a reconfiguration failure. After detecting a connectionfailure, the UE 102 may inform 508 the E-UTRAN 234 of the secondconnection 107 b failure. As will be described in detail below, the UE102 may inform 508 the E-UTRAN 234 of the second connection 107 bfailure by using the first connection 107 a or by using a re-establishedsecond connection (not shown). For example, if a suitable cell isdetected, the UE 102 may inform 508 the E-UTRAN 234 using there-established second connection (not shown). By comparison, if asuitable cell is not detected, the UE 102 may inform 508 the E-UTRAN 234using the first connection 107 a.

FIG. 6 is a flow diagram illustrating one configuration of a method 600for re-establishing a connection by an eNB 160. The eNB 160 may receive602 information about a failure of a second connection 107 b between theUE 102 and the E-UTRAN 234. For example, the second eNB 160 b mayreceive a connection re-establishment request message from the UE 102that indicates that a second connection 107 b has failed and thatidentifies the cause of the failure.

The eNB 160 may then determine 604 whether second connection UE contextinformation 198 b-c is stored on the eNB 160. For example, the secondeNB 160 b may determine 604 whether second connection UE contextinformation 198 b is stored on the second eNB 160 b.

The eNB 160 may re-establish 606 the second connection 107 b when secondconnection UE context information 198 b is stored on the eNB 160.Re-establishing 606 the second connection 107 b may include sending aconnection re-establishment message to the UE 102 as described inconnection with FIG. 2. In response, the UE 102 may send a connectionre-establishment complete message, and a second connection 107 b may bere-established. The eNB 160 may be configured so that if the eNB 160determines 604 that second connection UE context information 198 b-c isnot stored on the eNB 160, the eNB 160 does not re-establish 606 thesecond connection 107 b.

Once the second connection 107 b has been re-established, the eNB 160may inform 608 another eNB about the re-established second connectionwith the UE 102. For example, the second eNB 160 b may notify the firsteNB 160 a that a second connection 107 b has been re-established withthe UE 102.

FIG. 7 is a block diagram illustrating an addition of a secondconnection 707 b between a UE 702 and an eNB 760 b. The UE 702, eNBs 760a-d, cells 796 a-d, connections 707 a-b and UE context information 798a-c may be examples of corresponding elements described in connectionwith FIG. 1. To implement dual connectivity, the UE 702 may add a secondconnection 707 b. For example, the UE 702 having a first connection 707a with the first eNB 760 a may establish a second connection 707 b withthe second eNB 760. Before establishing the second connection 707 b, theE-UTRAN 234 may prepare and signal the second connection UE contextinformation 798 b to the second eNB 760 b. As described above, thesecond connection UE context information 798 b may be all, or part of,the first connection UE context information 798 a. The E-UTRAN 234 maythen signal the UE 702 to establish the second connection 707 b, forexample using the method 200 described in connection with FIG. 2.

FIG. 8 is a block diagram illustrating a handover of a second connectionbetween a UE 802 and multiple eNBs 860 b-c. The UE 802, eNBs 860 a-d,cells 896 a-d, connections 807 a-c and UE context information 898 a-cmay be examples of corresponding elements described in connection withFIG. 1. To maintain dual connectivity, the UE 802 may hand over thesecond connection 807 b. For example, the UE 802 having a firstconnection 807 a with the first eNB 860 a and a second connection 807 bwith the second eNB 860 b may change the cells pertaining to the secondconnection 807 b from the second cell 896 b to the third cell 896 c. Inother words, the second connection 807 b between the UE 802 and thesecond eNB 860 b may be replaced with a handed-over second connection807 c between the UE 802 and the third eNB 860 c. Before handing overthe second connection 807 b, and establishing the handed-over secondconnection 807 c, the E-UTRAN 234 may prepare and signal secondconnection UE context information 898 c to the third eNB 860 c forestablishing the handed-over second connection 807 c. As describedabove, the second connection UE context information 898 c may be all, orpart of, the first connection UE context information 898 a. The E-UTRAN234 may then signal the UE 802 to establish the handed-over secondconnection 807 c, for example using the method 200 described inconnection with FIG. 2.

FIG. 9 is a block diagram illustrating a failure of a second connection907 b between a UE 902 and an eNB 960 b. The UE 902, eNBs 960 a-d, cells996 a-d, connections 907 a-b and UE context information 998 a-c may beexamples of corresponding elements described in connection with FIG. 1.As described above, during dual connectivity, one of the connections mayexperience a connection failure, indicated in FIG. 9 by the box 949. Forexample, the second connection 907 b may experience a radio linkfailure, a handover failure, an E-UTRA mobility failure, an integritycheck failure or a reconfiguration failure as described in connectionwith FIG. 4. In this example, to maintain dual connectivity, the secondconnection 907 b may be re-established as described in connection withFIGS. 5 and 6.

FIG. 10 is a block diagram illustrating one configuration of an E-UTRAN1034 and a UE 1002 in which systems and methods for re-establishing aconnection may be implemented. The UE 1002, E-UTRAN 1034, UE contextinformation 1098 a-b, cells 1096 a-f and connections 1007 a-b may beexamples of corresponding elements described in connection with at leastone of FIGS. 1 and 2.

The E-UTRAN 1034 may include a PeNB 1060 a and an SeNB 1060 b. The UE1002 may communicate with the PeNB 1060 a via the first connection 1007a. The UE 1002 may communicate with the SeNB 1060 b via the secondconnection 1007 b. The PeNB 1060 a and SeNB 1060 b may be implemented inaccordance with the eNB 160 described in connection with FIG. 1.

The PeNB 1060 a may provide multiple cells 1096 a-c for connection toone or more UEs 1002. For example, the PeNB 1060 a may provide cell A1096 a, cell B 1096 b and cell C 1096 c. Similarly, the SeNB 1060 b mayprovide multiple cells 1096 d-f. The UE 1002 may be configured totransmit/receive on one or more cells (e.g., cell A 1096 a, cell B 1096b and cell C 1096 c) for the first connection 1007 a (e.g., a primary Uuinterface). The UE 1002 may also be configured to transmit/receive onone or more other cells (e.g., cell D 1096 d, cell E 1096 e and cell F1096 f) for the second connection 1007 b (e.g., a secondary Uuinterface). If the UE 1002 is configured to transmit/receive on multiplecells 1096 a-f for a radio connection 1007 a-b, a carrier aggregationoperation may be applied to the radio connection 1007 a-b.

The PeNB 1060 a may manage and store first connection UE contextinformation 1098 a for each UE 1002 using the configured cells 1096 a-c.In a similar fashion, the SeNB 1060 b may manage and store secondconnection UE context information 1098 b for each UE 1002 using theconfigured cells 1096 d-f. The PeNB 1060 a may also store and managesecond connection UE context information 1098 b. Accordingly, an eNB maybehave as both the PeNB 1060 a and the SeNB 1060 b.

One MAC entity 1025 a-b and one PHY entity 1027 a-b may be mapped to oneconnection 1007 a-b. For example, a first MAC entity 1025 a and a firstPHY entity 1027 a may be mapped to the first connection 1007 a.Similarly, a second MAC entity 1025 b and a second PHY entity 1027 b maybe mapped to the second connection 1007 b.

The UE 1002 may include an RRC entity 1023. The RRC entity 1023 mayreceive RRC messages (e.g., RRC connection re-establishment message,addition of connection command, handover command, etc.) from an RRCentity (not shown) of the E-UTRAN 1034. The RRC entity 1023 may alsotransmit RRC messages (e.g., RRC connection re-establishment requestmessage, RRC connection re-establishment complete message) to the RRCentity (not shown) of the E-UTRAN 1034. The RRC entity 1023 may alsostore the UE context information 1098 a-b.

It should be noted that the UE 1002 may not be required to be aware ofthe PeNB 1060 a and the SeNB 1060 b, as long as the UE 1002 is aware ofthe multiple Uu interfaces with the E-UTRAN 1034. In one configuration,the UE 1002 may see an eNB as a point on the E-UTRAN 1034. In anotherconfiguration, the UE 1002 may see the multiple Uu interfaces with theE-UTRAN 1034 as connections with multiple points on the E-UTRAN 1034. Inanother configuration, the E-UTRAN 1034 may provide multiple Uuinterfaces with the same or different eNBs. For instance, the PeNB 1060a and the SeNB 1060 b may be the same eNB. The multiple Uu interfaces(e.g., multi-connectivity) may be achieved by a single eNB. In otherwords, in one configuration, the systems and methods described hereinmay be achieved by a single eNB or a single scheduler. The UE 1002 maybe able to connect more than one Uux interface (e.g., Uu1, Uu2, Uu3,etc.). Each Uu interface may be used to perform carrier aggregation.Accordingly, the UE 1002 may be configured with more than one set ofserving cells in a carrier aggregation scenario.

It should be noted that while multiple Uu interfaces are described, thesystems and methods described herein may be realized by a single Uuinterface or a single radio connection depending on the definition ofinterface. For example, a radio interface may be defined as an interfacebetween the UE 1002 and the E-UTRAN 1034. In this definition, theinterface may not be an interface between the UE 1002 and the eNB. Forexample, one radio interface may be defined as an interface between theUE 1002 and the E-UTRAN 1034 with multi-connectivity. Accordingly, theUu interface and the Uux interface discussed above may be considered asdifferent characteristics of cells. For instance, the Uu interface maybe a first set of cell(s) and the Uux interface may be a second set ofcell(s). Also, the first radio interface may be rephrased as a first setof cell(s) and the second radio interface may be rephrased as a secondset of cell(s).

FIG. 11 is a block diagram illustrating one configuration of a UE 1102and multiple eNBs 1160 a-d in which systems and methods forre-establishing a connection may be implemented. More specifically, FIG.11 depicts re-establishing a second connection with a serving cell or asource cell. The UE 1102, eNBs 1160 a-d, cells 1196 a-d, connections1107 a-c and UE context information 1198 a-c may be examples ofcorresponding elements described in connection with FIG. 1.Re-establishing a connection with a serving cell may be triggered by aradio link failure, an addition of connection failure, an integritycheck failure or a reconfiguration failure. Re-establishing a connectionwith a source cell may be triggered by a handover failure.

An example of re-establishing a connection with a serving cell is givenas follows. The UE 1102 may have a second connection 1107 b with thesecond eNB 1160 b. In other words, the second cell 1196 b may be aserving cell for the second connection 1107 b. Upon detecting a failure1149 of the second connection 1107 b, the UE 1102 may select a suitablecell (e.g., the second cell 1196 b) and try to obtain a re-establishedsecond connection 1107 c with the second eNB 1160 b.

An example of re-establishing a connection with a source cell is givenas follows. The UE 1102 may have a second connection 1107 b with thesecond eNB 1160 b. The UE 1102 may attempt to hand over the secondconnection 1107 b from the second cell 1196 b to the third cell 1196 c.In other words, the second cell 1196 b may be a source cell for thesecond connection 1107 b. Upon detecting a handover failure 1149 of thesecond connection 1107 b, the UE 1102 may select a suitable cell (e.g.,the second cell 1196 b) and try to obtain a re-established secondconnection 1107 c with the second eNB 1160 b.

FIG. 12 is a block diagram illustrating one configuration of a UE 1202and multiple eNBs 1260 a-d in which systems and methods forre-establishing a connection may be implemented. More specifically, FIG.12 depicts re-establishing a second connection with a non-serving cellor a target cell. The UE 1202, eNBs 1260 a-d, cells 1296 a-d,connections 1207 a-c and UE context information 1298 a-c may be examplesof corresponding elements described in connection with FIG. 1.Re-establishing a connection with a non-serving cell may be triggered bya radio link failure, a connection addition failure, an integrity checkfailure or a reconfiguration failure. Re-establishing a connection witha target cell may be triggered by a handover failure.

An example of re-establishing a connection with a non-serving cell isgiven as follows. The UE 1202 may have a second connection 1207 b withthe second eNB 1260 b. In other words, the second cell 1296 b may be aserving cell for the second connection 1207 b. Accordingly, the thirdcell 1296 c may be a non-serving cell. Upon detecting a failure 1249 ofthe second connection 1207 b, the UE 1202 may select a suitable cell(e.g., the third cell 1296 c) and try to obtain a re-established secondconnection 1207 c with the third eNB 1260 c.

An example of re-establishing a connection with a target cell is givenas follows. The UE 1202 may have a second connection 1207 b with thesecond eNB 1260 b. The UE 1202 may attempt to hand over the secondconnection 1207 b from the second cell 1296 b to the third cell 1296 c.In other words, the second cell 1296 b may be a source cell for thesecond connection 1207 b and the third cell 1296 c may be a target cellfor the second connection 1207 b. Upon detecting a handover failure 1249of the second connection 1207 b, the UE 1202 may select a suitable cell(e.g., the third cell 1296 c) and try to obtain a re-established secondconnection 1207 c with the third eNB 1260 c.

FIG. 13 is a block diagram illustrating one configuration of a UE 1302and multiple eNBs 1360 a-d in which systems and methods forre-establishing a connection may be implemented. The UE 1302, eNBs 1360a-d, cells 1396 a-d, connections 1307 a-b and UE context information1398 a-c may be examples of corresponding elements described inconnection with FIG. 1. As described above, a suitable cell may not bedetected or selected. In these examples, the UE 1302 may notify theE-UTRAN 234 of the failure of the second connection 1307 b via the firstconnection 1307 a. An example is given as follows. A UE 1302 configuredwith a first connection 1307 a and a second connection 1307 b may detecta failure 1349 of the second connection 1307 b. The UE 1302 may thenselect a suitable cell (e.g., the fourth cell 1396 d) and try to obtaina re-established second connection with the fourth eNB 1360 d. Asillustrated by this example, the UE 1302 may select a non-prepared cell(e.g., the fourth cell 1396 d) as a suitable cell. However, are-established second connection may not be established because thefourth eNB 1360 d does not include UE context information. In otherwords, the fourth cell 1396 d may not be a prepared cell forre-establishment and the UE 1302 may release the second connection 1307b.

In another example, the UE 1302 may avoid trying to obtain are-established second connection with the fourth cell 1396 d. Forexample, if the UE 1302 has determined that the fourth cell 1396 d isnot a prepared cell, the UE 1302 may avoid trying to obtain are-established second connection with the fourth eNB 1360 d. Asdescribed above, the UE 1302 may have determined that the fourth cell1396 d is not a prepared cell based on the prepared re-establishmentcandidate cells list.

In one example, if the UE 1302 does not find any suitable cell from theprepared re-establishment candidate cells list, the UE 1302 may informthe first eNB 1360 a of the failure of the second connection 1307 b, asindicated by the arrow 1351. The first eNB 1360 a may then check the UEcontext information 1398 a stored on the first eNB 1360 a and may informthe second eNB 1360 b of the released second connection 1307 b.

FIG. 14 is a flow diagram illustrating a more specific configuration ofa method 1400 for re-establishing a connection by a UE 102. The UE 102may establish 1402 a first connection 107 a between the UE 102 and anE-UTRAN 234. This may be done as described in connection with FIG. 5.

The UE 102 may establish 1404 a second connection 107 b between the UE102 and the E-UTRAN 234. This may be done as described in connectionwith FIG. 5.

The UE 102 may detect 1406 a failure of the second connection 107 b.This may be done as described in connection with FIG. 5.

The UE 102 may select 1408 a suitable cell for a re-established secondconnection 1107 c from a prepared re-establishment candidate cells list.As described above, the E-UTRAN 234 may provide a preparedre-establishment candidate cells list that includes cells that haveaccess to second connection UE context information 198 b-c. A cell 196may have access to second connection UE context information 198 b-c ifthe eNB 160 that provides the cell 196 stores second connection UEcontext information 198 b-c. The list may be signaled to the UE 102 viaRRC messaging or broadcast messaging.

From this list, the UE 102 may select 1408 a suitable cell. In someexamples, the suitable cell may be a source cell or a target cell(relating to a handover failure) or a serving cell or a non-serving cell(relating to a radio link failure or an addition of connection failure).

During selection of a suitable cell, the UE 102 may determine 1410 ifthe suitable cell is detected. For example, the UE 102 may determinewhether a measured RSRP of a cell may be fulfilled with (or satisfy) acell selection criterion, etc. If the UE 102 determines 1410 that asuitable cell is detected, the UE 102 may inform 1412 the suitable cellof the second connection failure. For example, the UE 102 may send aconnection re-establishment request message as described in connectionwith FIG. 2. As a result, a re-established second connection 1107 c maybe obtained.

By comparison, if the UE 102 determines 1410 that a suitable cell is notdetected, the UE 102 may inform 1416 a cell 196 of the first connectionabout the second connection failure. For example, the UE 102 may informthe first eNB 160 a about the failure of the second connection 107 b.The UE 102 may then release 1418 the second connection 107 b. In thisexample, the first eNB 160 a may notify the second eNB 160 b of therelease of the second connection 107 b.

FIG. 15 is a flow diagram illustrating a more specific configuration ofa method 1500 for re-establishing a connection by an eNB 1160. The eNB1160 may prepare 1502 UE context information 1198 a-c for there-established second connection 1107 c. As described above, are-established second connection 1107 c may be established if a suitablecell with UE context information 1198 a-c is detected. Accordingly,before instructing a UE 1102 to perform a handover, or add a newconnection, the eNB 1160 may provide UE context information 1198 a-c toone or more cells, rendering those cells prepared cells. In someimplementations, the eNB 1160 may signal UE context information 1198 a-cto eNBs where there is the potential to be a connection failure in theregion.

The eNB 1160 may then receive 1504 information about a failure of thesecond connection 1107 b between the UE 1102 and the E-UTRAN 234. Thismay be done as described in connection with FIG. 6.

The eNB 1160 may provide 1506 a prepared re-establishment candidatecells list for a re-established second connection 1107 c. As describedabove, the E-UTRAN 234 may provide one or more cells with UE contextinformation 1198 a-c. Accordingly, the cells with the UE contextinformation 1198 a-c are prepared to re-establish a second connection.The eNB 1160 may compile a list of these prepared cells, and signal thelist to the UE 1102, via RRC messaging for example.

The eNB 1160 may determine 1508 whether second connection UE contextinformation 1198 b-c is stored on the eNB 1160. This may be done asdescribed in connection with FIG. 6.

The eNB 1160 may re-establish 1510 the second connection when secondconnection UE context information 1198 b-c is stored on the eNB 1160.This may be done as described in connection with FIG. 6.

The eNB 1160 may inform 1512 another eNB of the E-UTRAN 234 about there-established second connection 1107 c. This may be done as describedin connection with FIG. 6.

FIG. 16 is a thread diagram illustrating one configuration 1600 forre-establishing a connection. The UE 1602, first cell 1696 a, the secondcell 1696 b, first connection 1607 a and second connection 1607 b may beexamples of corresponding elements described in connection with FIG. 1.In some examples, the first cell 1696 a may be provided by an eNB 160.The second cell 1696 b may be provided by the same, or a different eNB160. As described above, the second connection 1607 b may experience aconnection failure. In this example, the UE 1602 may select 1609 asuitable cell (e.g., the second cell 1696 b) from cells listed in aprepared re-establishment candidate cells list and may attempt tore-establish the second connection 1607 b. For example, the UE 1602 mayevaluate a cell listed in the prepared re-establishment candidate cellslist in a certain priority order and the UE 1302 may determine if it isa suitable cell (e.g., based on the RSRP of the cell). Then if asuitable cell belonging to the prepared re-establishment candidate cellslist is found, the UE 1602 may inform the suitable cell (i.e., an eNB)about the failure of the second connection 1607 b.

The UE 1602 may then send 1611 a connection re-establishment requestmessage to the second cell 1696 b (i.e., an eNB). This may be done asdescribed in connection with FIG. 2. Sending 1611 a connectionre-establishment request message may include setting the contents of theconnection re-establishment message. An example is given as follows.

The UE 1602 may set a ue-Identity in the connection re-establishmentmessage as follows. The UE 1602 may set a cell Radio Network TemporaryIdentifier (C-RNTI) field to the C-RNTI used in the source cell (e.g.,PCell) of the second connection 1607 b for a handover failure, or inother cases, to the C-RNTI used in the cell of the second connection1607 b (e.g., PCell) in which the trigger for the re-establishmentoccurred. The UE 102 may set a physCellId field to the physical cellidentity of the source cell (e.g., PCell) of the second connection 1607b for a handover failure, or of the cell (e.g., PCell) of the secondconnection 1607 b in which the trigger for the re-establishmentoccurred. The UE 1602 may set a shortMAC-I field to the 16 leastsignificant bits of the MAC-I calculated. The UE 1602 may also set areestablishmentCause field as follows. If the re-establishment procedurewas initiated due to reconfiguration failure, the UE 1602 may set thereestablishmentCause field to the value reconfigurationFailure. If there-establishment procedure was initiated due to a handover failure, theUE 1602 may set the reestablishmentCause field to the valuehandoverFailure. For other cases, the UE 1602 may set thereestablishmentCause field to the value otherFailure. The UE 1602 maythen submit the connection re-establishment request message to a lowerlayer of the UE 1602 (e.g., at least one of the PDCP, the RLC, the MACor the PHY layer) of the second connection for transmission.

The second cell 1696 b (i.e., an eNB) may then send 1613 a connectionre-establishment message. This may be done as described in connectionwith FIG. 2.

In response, the UE 1602 may send 1615 a connection re-establishmentcomplete message. This may be done as described in connection with FIG.2.

FIG. 17 is a thread diagram illustrating another configuration 1700 forre-establishing a connection. The UE 1702, first cell 1796 a, secondcell 1796 b, first connection 1707 a and second connection 1707 b may beexamples of corresponding elements described in connection with FIG. 1.The first cell 1796 a may be provided by an eNB. The second cell 1796 bmay be provided by the same, or a different eNB. As described above, insome cases, the second connection 1707 b may experience a connectionfailure. In this example, the UE 1702 may attempt to select 1709 asuitable cell from cells listed in a prepared re-establishment candidatecells list and may attempt to re-establish the second connection 1707 bwith the second cell 1796 b. If a suitable cell cannot be selected 1709,the UE 1702 may release 1711 the second connection. Accordingly, the UE1702 may send 1713 a second connection failure message to the secondcell 1796 b indicating to the second cell 1796 b (i.e., to an eNB) thatthe second connection has failed and been released.

FIG. 18 illustrates various components that may be utilized in a UE1802. The UE 1802 described in connection with FIG. 18 may beimplemented in accordance with the UE 102 described in connection withFIG. 1. The UE 1802 includes a processor 1829 that controls operation ofthe UE 1802. The processor 1829 may also be referred to as a centralprocessing unit (CPU). Memory 1835, which may include read-only memory(ROM), random access memory (RAM), a combination of the two or any typeof device that may store information, provides instructions 1831 a anddata 1833 a to the processor 1829. A portion of the memory 1835 may alsoinclude non-volatile random access memory (NVRAM). Instructions 1831 band data 1833 b may also reside in the processor 1829. Instructions 1831b and/or data 1833 b loaded into the processor 1829 may also includeinstructions 1831 a and/or data 1833 a from memory 1835 that were loadedfor execution or processing by the processor 1829. The instructions 1831b may be executed by the processor 1829 to implement one or more of themethods and procedures 500 and 1400 described above.

The UE 1802 may also include a housing that contains one or moretransmitters 1858 and one or more receivers 1820 to allow transmissionand reception of data. The transmitter(s) 1858 and receiver(s) 1820 maybe combined into one or more transceivers 1818. One or more antennas1822 a-n are attached to the housing and electrically coupled to thetransceiver 1818.

The various components of the UE 1802 are coupled together by a bussystem 1841, which may include a power bus, a control signal bus and astatus signal bus, in addition to a data bus. However, for the sake ofclarity, the various buses are illustrated in FIG. 18 as the bus system1841. The UE 1802 may also include a digital signal processor (DSP) 1837for use in processing signals. The UE 1802 may also include acommunications interface 1839 that provides user access to the functionsof the UE 1802. The UE 1802 illustrated in FIG. 18 is a functional blockdiagram rather than a listing of specific components.

FIG. 19 illustrates various components that may be utilized in an eNB1960. The eNB 1960 described in connection with FIG. 19 may beimplemented in accordance with the eNB 160 described in connection withFIG. 1. The eNB 1960 includes a processor 1929 that controls operationof the eNB 1960. The processor 1929 may also be referred to as a centralprocessing unit (CPU). Memory 1935, which may include read-only memory(ROM), random access memory (RAM), a combination of the two or any typeof device that may store information, provides instructions 1931 a anddata 1933 a to the processor 1929. A portion of the memory 1935 may alsoinclude non-volatile random access memory (NVRAM). Instructions 1931 band data 1933 b may also reside in the processor 1929. Instructions 1931b and/or data 1933 b loaded into the processor 1929 may also includeinstructions 1931 a and/or data 1933 a from memory 1935 that were loadedfor execution or processing by the processor 1929. The instructions 1931b may be executed by the processor 1929 to implement one or more of themethods and procedures 600 and 1500 described above.

The eNB 1960 may also include a housing that contains one or moretransmitters 1917 and one or more receivers 1978 to allow transmissionand reception of data. The transmitter(s) 1917 and receiver(s) 1978 maybe combined into one or more transceivers 1976. One or more antennas1980 a-n are attached to the housing and electrically coupled to thetransceiver 1976.

The various components of the eNB 1960 are coupled together by a bussystem 1941, which may include a power bus, a control signal bus and astatus signal bus, in addition to a data bus. However, for the sake ofclarity, the various buses are illustrated in FIG. 19 as the bus system1941. The eNB 1960 may also include a digital signal processor (DSP)1937 for use in processing signals. The eNB 1960 may also include acommunications interface 1939 that provides user access to the functionsof the eNB 1960. The eNB 1960 illustrated in FIG. 19 is a functionalblock diagram rather than a listing of specific components.

FIG. 20 is a block diagram illustrating one configuration of a UE 2002in which systems and methods for re-establishing a connection may beimplemented. The UE 2002 includes transmit means 2043, receive means2045 and control means 2047. The transmit means 2043, receive means 2045and control means 2047 may be configured to perform one or more of thefunctions described in connection with FIGS. 5 and 14 above. FIG. 18above illustrates one example of a concrete apparatus structure of FIG.20. Other various structures may be implemented to realize one or moreof the functions of FIGS. 5 and 14. For example, a DSP may be realizedby software.

FIG. 21 is a block diagram illustrating one configuration of an eNB 2160in which systems and methods for re-establishing a connection may beimplemented. The eNB 2160 includes transmit means 2143, receive means2145 and control means 2147. The transmit means 2143, receive means 2145and control means 2147 may be configured to perform one or more of thefunctions described in connection with FIGS. 6 and 15 above. FIG. 19above illustrates one example of a concrete apparatus structure of FIG.21. Other various structures may be implemented to realize one or moreof the functions of FIGS. 6 and 15. For example, a DSP may be realizedby software.

The term “computer-readable medium” refers to any available medium thatcan be accessed by a computer or a processor. The term“computer-readable medium,” as used herein, may denote a computer-and/or processor-readable medium that is non-transitory and tangible. Byway of example, and not limitation, a computer-readable orprocessor-readable medium may comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code in the form of instructions or data structures and that canbe accessed by a computer or processor. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray® disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.

It should be noted that one or more of the methods described herein maybe implemented in and/or performed using hardware. For example, one ormore of the methods described herein may be implemented in and/orrealized using a chipset, an application-specific integrated circuit(ASIC), a large-scale integrated circuit (LSI) or integrated circuit,etc.

Each of the methods disclosed herein comprises one or more steps oractions for achieving the described method. The method steps and/oractions may be interchanged with one another and/or combined into asingle step without departing from the scope of the claims. In otherwords, unless a specific order of steps or actions is required forproper operation of the method that is being described, the order and/oruse of specific steps and/or actions may be modified without departingfrom the scope of the claims.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the systems, methods and apparatus described herein withoutdeparting from the scope of the claims.

What is claimed is:
 1. A user equipment (UE) for dual connectivity,comprising: a processor; and memory in electronic communication with theprocessor, wherein instructions stored in the memory are executable to:establish, by the UE, a first media access control (MAC) entity for afirst set of cells of the UE and a second MAC entity for a second set ofcells of the UE for dual connectivity; and inform, by the UE, by usingthe first set of cells, a wireless communication device of a failure ofthe second set of cells when a failure of the second set of cells isdetected by the UE, wherein the failure of the second set of cellsincludes a radio link failure of the second set of cells, the radio linkfailure is detected based on a certain amount of consecutive out-of-syncindications of a certain cell from a physical layer of the UE, thefailure of the second set of cells is detected by the UE, while thefirst set of cells and the second set of cells are configured for thedual connectivity for the UE, and the wireless communication device isinformed of the failure of the second set of cells, while the first setof cells and the second set of cells are configured for the dualconnectivity for the UE.
 2. A method by a user equipment (UE) for dualconnectivity, comprising: establishing, by the UE, a first media accesscontrol (MAC) entity for a first set of cells of the UE and a second MACentity for a second set of cells of the UE for dual connectivity; andinforming, by the UE, by using the first set of cells, a wirelesscommunication device of a failure of the second set of cells when afailure of the second set of cells is detected by the UE, wherein thefailure of the second set of cells includes a radio link failure of thesecond set of cells, the radio link failure is detected based on acertain amount of consecutive out-of-sync indications of a certain cellfrom a physical layer of the UE, the failure of the second set of cellsis detected by the UE, while the first set of cells and the second setof cells are configured for the dual connectivity for the UE, and thewireless communication device is informed of the failure of the secondset of cells, while the first set of cells and the second set of cellsare configured for the dual connectivity for the UE.
 3. A wirelesscommunication device for dual connectivity, comprising: a processor; andmemory in electronic communication with the processor, whereininstructions stored in the memory are executable to: send, by thewireless communication device, information which causes a first set ofcells for a first media access control (MAC) entity of a user equipment(UE) and a second set of cells for a second MAC entity of the UE to beestablished for dual connectivity; and receive, from the UE, by usingthe first set of cells, information about a failure of the second set ofcells when a failure of the second set of cells is detected by the UE,wherein the failure of the second set of cells includes a radio linkfailure of the second set of cells, the radio link failure is detectedbased on a certain amount of consecutive out-of-sync indications of acertain cell from a physical layer of the UE, the failure of the secondset of cells is detected by the UE, while the first set of cells and thesecond set of cells are configured for the dual connectivity for the UE,and the information about the failure of the second set of cells isreceived, while the first set of cells and the second set of cells areconfigured for the dual connectivity for the UE.
 4. A method by awireless communication device for dual connectivity, comprising:sending, by the wireless communication device, information which causesa first set of cells for a first media access control (MAC) entity of auser equipment (UE) and a second set of cells for a second MAC entity ofthe UE to be established for dual connectivity; and receiving, from theUE, by using the first set of cells, information about a failure of thesecond set of cells when a failure of the second set of cells isdetected by the UE, wherein the failure of the second set of cellsincludes a radio link failure of the second set of cells, the radio linkfailure is detected based on a certain amount of consecutive out-of-syncindications of a certain cell from a physical layer of the UE, thefailure of the second set of cells is detected by the UE, while thefirst set of cells and the second set of cells are configured for thedual connectivity for the UE, and the information about the failure ofthe second set of cells is received, while the first set of cells andthe second set of cells are configured for the dual connectivity for theUE.